This invention relates to an outboard jet drive for a watercraft and more particularly to an improved drive of this type.
There have been proposed types of outboard jet drives for watercraft which are basically similar to an outboard motor having a propeller. However, rather than incorporating a propeller in the lower unit, the jet drive includes a jet pump in the lower unit that operates so as to provide a propulsion force for the watercraft.
As is known, there are some advantages in employing such jet pumps for propulsion units as opposed to propellers. Conventionally, the jet drive permits operation in shallower water and also, because the impeller is shrouded, there is less likelihood of injury.
However, the flow of water into the water inlet of the jet pump is very important in the performance of the watercraft. If the jet pump has its water inlet disposed rearwardly of the transom, as is typical with outboard motor practice, then cavitation can occur. That is, the undersurface of the hull at the transom gives rise to a parting of the water, which will direct the water away from the inlet of the jet pump and cause cavitation and loss of performance.
Although various proposed constructions have been suggested for positioning the jet pump forwardly relative to the transom, there still exists some gap between the underside of the hull to the rear of the transom and the water inlet opening of the jet propulsion unit that can give rise to this cavitation.
It is, therefore, a principal object of this invention to provide an improved jet propulsion out drive unit for a watercraft wherein the jet pump can operate more efficiently.
It is a further object of this invention to provide an outboard jet propulsion unit for a watercraft wherein the water inlet of the jet pump is actually disposed beneath the hull of the watercraft to improve pumping efficiency.
The very nature of jet propulsion units, which permits them to operate in shallow water, gives rise to certain ancillary problems. Because these units can be utilized in shallow water, they are so used as a result. Frequently the water inlet opening of the jet pump can become clogged. With an outboard motor it is possible to tilt the outboard motor up about its tilt and trim axis and access the propeller for clearing it. With a jet propulsion unit, however, the water inlet opening to the jet propulsion unit normally faces downwardly, and when the outboard drive is tilted up, the water inlet opening will be not only spaced further rearwardly from the transom, but also will face away from the transom, making cleaning difficult.
It is, therefore, a still further object of this invention to provide an improved jet propulsion unit for a watercraft wherein the jet propulsion unit can be easily accessed for servicing.
It is another object of this invention to provide an improved jet propulsion unit for a watercraft wherein the water inlet opening of the jet pump can be easily swung up for access.